Abstract/Project Summary This application is being submitted in response to NOT-CA-19-028 Administrative Supplements for Activities to Promote Human Immune-Representing Oncology Models as a supplement to our parent grant R01CA239261. The goal of the parental grant is to elucidate the relationship between chronic IFN-I signaling, inflammation, immune exhaustion, and the development of an immuno-suppressive tumor niche that favors tumor growth. To achieve this goal, we will utilize a humanized mouse model that 1) allows engraftment and growth of multiple tumor cell lines and 2) recapitulates IFN-I induced immune activation and exhaustion during chronic HIV infection in vivo. We will utilize novel strategies to promote or block IFN-I signaling in vivo and an innovative approach to specifically generate tumor specific T cells to: (1) define the precise contribution of IFN- I signaling during HIV infection to the development of immuno-suppressive tumor environment and exhaustion of anti-tumor T cell that favor cancer growth; and (2) investigate if blocking chronic IFN-I signaling during chronic HIV infection can improve anti-tumor immunity and efficacy of immune checkpoint inhibitor blockade. In the current supplemental application, our group proposes to evaluate potential alternative approaches to the use of fetal tissue in the generation of humanized mice, and to compare results with those obtained using the fetal-tissue-dependent BLT model that our parental grant is based upon. In particular, we will focus on in vivo testing of our recently published ?artificial thymic organoid? (ATO) model and its potential to serve as an alternative to Thy/Liv implants in BLT mice in the production of functional mature human T cells in the context of the parental grant. These studies could provide a basis for further investigation in this grant and in other projects for the use of a non-fetal tissue derived humanized mouse model.